The invention is related to a process chamber and a method for processing a material by a directed beam of electromagnetic radiation, in particular for a laser sintering device.
A laser sintering device comprises in a known manner a laser and a process chamber, in which the object to be manufactured is built, as well as a coupling window for coupling the laser beam into the process chamber.
When the laser locally hits the powder material and when the powder material is heated, an evaporation of small amounts of material may occur. In the process the evaporated material or constituents of the same or also chemical reaction products as well as dust particles suspended in the atmosphere of the process chamber deposit at the coupling window. This leads to a reduction of the transparency of the coupling window and accordingly to a decrease of the intensity of the laser beam.
From WO 97/06918 a laser sintering device is known, in which a nozzle for introducing a gas for blowing the coupling window is provided, which is annularly surrounding the coupling window on the side of the coupling window facing the process chamber. The gas flow is tangentially to the surface of the coupling window.
However, in the known device the surface of the coupling window does not stay clean all over. Also, temperature gradients between the coupling window and the blowing gas on the one hand and the gas within the process chamber on the other hand may lead to interfering beam deflections. The blowing gas may be supplied from a single side in order to alleviate the second problem. However, this leads to a more rapid deposition of dirt on the top surface of the coupling window.
From DE 198 53 947 C1 a process chamber for selective laser melting is known, wherein a protective gas is introduced into the process chamber via a first inlet, so that it flows across the working surface. Also, second inlets for a second lighter gas, which is annularly supplied, are provided in an elevated region of the process chamber, where the coupling window is located. Thereby, within the elevated region a kind of buffer volume of the second lighter gas is formed, by which vapours that are produced in the work zone are kept away from the coupling window. However, the problem of an interfering beam deflection due to a temperature gradient is not solved by this.